The present invention relates to diaphragm used in shut-off valves and regulators and more particularly to an improved spring diaphragm for shut-off valves and regulators for the hermetic separation of adjacent chambers of valves under pressure, as well as for the possibility of regulating the magnitude of the flow passing through a pipeline.
The spring diaphragm according to the invention is of unique construction, which will be referred to hereinafter as "two-storey diaphragm", can be employed in devices used in water-supply systems and in pipelines transporting petroleum, gas, various kinds of acids and bases, and other liquid mixtures and solutions.
A diaphragm which is intended for similar purposes and can be employed in similar devices is known (see "Fluid Controlling Diaphragm Valve," England, Classes: 135, Fick 7/16, No. 34131).
This diaphragm has the form a disk of molded shape made of rubber, at its center there is provided a bolt for joining the diaphragm to an actuator.
The outer shape of the diaphragm repeats the shape of the inner surface of the valve body, and the inner surface of the diaphragm corresponds to the outer surface of the actuator.
The top of the actuator is connected to a screw, which is screwed into a bushing, on which a handwheel is fixedly attached.
The ascent of the diaphragm into the upper position and its descent into its lower position are effected by rotating the handwheel in the clockwise and counterclockwise directions.
Hermetic sealing of the valve (separation of the entrance and exit chambers) is effected by tightly compressing the diaphragm against the surface of the valve body with the aid of the actuator.
One deficiency of such diaphragm is the fact that it can be operated (the valve can be opened and closed) only by manual control and can be employed only in shut-off valves.
Such a diaphragm design cannot be employed in regulator valves, i.e., in devices which automatically regulate the value of the pressure or pressure drop.
Another shortcoming of the design of this diaphragm is the fact that its operation requires a manual drive mechanism that includes several parts (an actuator, a screw, a bushing, and a handwheel), which increases the weight of the valve and the amount of work going into its manufacture and reduces the lifetime of the valve and its reliability during service.
The diaphragm design described in U.S. Pat. No. 2,302,930 which can be employed in similar devices for similar purposes, is also known. The design of this diaphragm is in the form of an elastic disk which transforms into a spherical surface. On the convex side of the spherical surface, which comes into contact with the surface of the valve body, there are hermetically sealing bands arranged along the perimeter of the elastic disk, which are joined to one another by an hermetically sealing band located on the symmetry axis of the diaphragm.
This diaphragm provides for valve operation (opening and closing) using an hydraulic drive mechanism and a metallic restoring spring placed over the diaphragm. A valve with a diaphragm of such construction opens (the diaphragm rises into the upper position) when there is positive pressure below the diaphragm. The valve closes (the diaphragm drops into the lower position until contact is made with the valve body) either under the action of the restoring spring (in the absence of pressure in the pipeline system) or when a pressure is supplied to the chamber above the diaphragm. When the pressures above and below the diaphragm are equal, the latter descends under the action of the restoring force of the metallic spring.
One deficiency of this diaphragm is the fact that at low pressure drops and low flow rates the presence of the metallic spring creates vibrations, which rapidly destroy the diaphragm and render the valve ineffective.
Another deficiency of this design is the fact that the restoring force of the spring must be overcome to completely open the valve, and, as a result, there is an increase in the value of the minimal pressure needed to completely open the valve.
A third deficiency of this design is the presence of the spring and its seat, which complicates the design of the valve as a whole and its assembly and shortens the lifetime of both the diaphragm and the valve as a whole.
The diaphragm described in Israeli Application No. 62466 (Improved Diaphragm for Valves, Apr. 30, 1993) is also known. Its appearance resembles the diaphragm described in U.S. Pat. No. 2,302,930; however, this diaphragm is distinguished by the presence of radial and annular ribs on its concave surface, which perform the role of a metallic spring and replace the latter.
This diaphragm eliminates all the deficiencies described above and has several significant advantages over them.
This diaphragm design is very efficient when it is employed in valves with through apertures of relatively small nominal diameters (from 1/2" to 8").
In valves with larger nominal apertures (more than 8") there is a sharp increase in the active area of the diaphragm, which, in turn, requires an increase in the geometric dimensions (width and height) of the ribs arranged on the concave surface of the diaphragm.
One deficiency of this technical solution is the need to increase the minimal pressure required to open the valve, i.e., the hydraulic characteristics of the valve become poorer.